Under the spotlight: Blair during his time as Prime Minister (Image: Reuters)

A source close to Mr Bower said: “He is leaving no stone unturned, he is ­determined that this book will be ­explosive and a ­bestseller. It will look at every aspect of Blair’s life, from his time in office to his ­relationship with Wendi.

“It promises to be ­absolutely fascinating.

“The Wendi and Blair story was huge when it broke. It’s likely there will be even more information which will come out now.

“It will also go into his friendship and fall-out with Gordon Brown.

“It promises to be very juicy indeed.

“There will obviously also be anecdotes about Tony’s marriage to Cherie and the furore that surrounded Labour sending British troops out to the Iraq war.”

Mr Bower has written unauthorised biographies of Mr Brown, Mohamed al-Fayed, Virgin boss Sir Richard Branson and the late newspaper owner Robert Maxwell.

His book about Mr Cowell exposed the love affair with former X Factor judge Dannii Minogue as well as his behind-the-scenes rows with Gary Barlow. The book, Sweet Revenge: The ­Intimate Life of Simon Cowell, was written with the music mogul’s co-operation.

Mr Blair is not believed to have agreed to co-operate with the biography.